The present invention generally relates to industrial blowers. More particularly, the present invention relates to a high-speed, belt-driven blower having an improved spindle assembly and an air cooling system in order to cool various components of the blower and improve the reliability and durability of the blower.
Compact belt-driven centrifugal blowers are commonly used in air drying and blow-off applications. These types of applications include aqueous-based in-line process cleaners which are used in a variety of manufacturing industries, consisting of wash and blow-off/dry cycles all in one self-contained machine. Other applications include ultra-high performance air knives, high volume blow-off, and de-watering applications typical with canning, beverage and electronic industries. Such blowers are also used in air evacuation, aeration and large fluidized beds. Advantages of the belt-driven centrifugal blowers are primarily improved efficiency over other types of blowers, such as so-called regenerative blowers, and perhaps just as important, the ability to maintain pressure delivery at the more useful higher flowrates.
Current blower products are all very similar in design and performance, and all suffer from the same performance limitations. One such design plan is the containment of the high-speed impeller spindle assembly (bearing) housing within the compressed-air collector housing. Understanding that air compression necessarily raises the process gas (air) temperature, the spindle housing and thus the critical high-speed bearing elements are exposed directly to the hotter compressed-air stream, limiting not only delivery pressures (i.e., gas or air temperature rise) but also the ability to manage thermal dissipation in the critical precision bearing elements. Increased bearing operating temperature has been shown to reduce overall life, shorten lubricant life and pose limitations on speed. As a rule, a 20° F. rise in operating temperature will generally reduce lubricant life by a factor of one-half. All of the current art products incorporate this design, and hence all suffer from the same shortcomings. As such, current art designs employ larger diameter impeller wheels, offsetting with slower rotational operating speeds. This scheme, unfortunately, reduces specific speed of the compressor machinery aspect with the adjunct result of reducing compressor efficiency. Reduced compressor efficiency, on the other hand, leads directly to increased drive power requirements (hence more load and heat generated within bearings, belt and idler) and increased discharge gas-air temperatures, resulting in even less cooling efficacy.
For the same reasoning, durability and life of the drive belt and the belt tensioning system, which consists of a bearing equipped idler pulley assembly, can also be extended if temperature rise in these components can be appropriately managed. Belt manufacturers, in fact, state that an 18° F. operating temperature rise within the belt may reduce life by a factor of one-half. Further, a 36° F. ambient temperature rise is sufficient to cause this 18° temperature rise. Thus, the ability to manage temperature within the drive belt assembly can be shown to promote longevity of the drive system proper.
The manufacturers which produce high-speed, belt-driven blowers (compressor) products employ either identical or very similar designs for the high-speed spindle arrangement. It should be noted that “high-speed” typically means speed ranges from 12,000 to 20,000 RPM, with new art arrangements having speeds up to 28,000 RPM. A typical prior art arrangement is depicted in FIGS. 1A and 1B. Such can be described as a simple two-bearing design with spring pre-load.
With reference to FIGS. 1A and 1B, the spindle assembly 1 includes a pulley 2 attached to a shaft 3 which extends to an impeller 4 of a centrifugal compressor of the blower device. Bearing elements 5 and 6 are spaced from one another and disposed between the shaft 3 and the housing 7. A spring 8 is used to pre-load at either end of the arrangement, at the pulley side in FIG. 1A, and at the impeller side in FIG. 1B.
It is common to position the spring 8 on the pulley side (as illustrated in FIG. 1), in the event that axial loads applied at the impeller 4 cause additional compression, with impeller movement away from any closely positioned housing surface. This effectively inhibits a “crash” of the impeller 4. Even so, any applied axial load which is sufficient to compress the spring 8 beyond its pre-loaded working height will effectively “unload” the bearing element 5 or 6 on the opposite end, leading to instability and potential failure. Since the spring 8 is typically linear in its response, the only way to prevent this occurrence is to incorporate additional pre-load, or, to position the spring 8 such that the opposite bearing 5 or 6 is the only bearing that carries any axial (thrust) load. Predicting and controlling thrust loads, due to aerodynamic characteristics of the impeller 4, is very difficult and highly dependent on the operating point of the compressor. In fact, even for the same compressor, thrust load direction may shift from one direction to the other simply by shifting to a different flow-pressure operating point.
Attempts to compensate for the un-loading of the opposite bearing, instability and rapid failures described above, by increasing spring pre-load of the spindle assemblies of prior art results in reduced operating life due to additional pre-load. Typical operating life for current art systems range from under 2,000 to approximately 6,000 hours, or less than one year if operating on a continuous basis.
Positioning the spring at the pulley end, which is typical, is potentially troublesome as the heavy belt load, considering applied radial loads, attempts to misalign the bearing races of the bearing elements 5 and 6 at the adjacent bearing, and hence “skew” the ball track. The spring 8 is the only functioning part of the system 1 which can apply sufficient axial load to maintain this alignment. Increasing spring pre-load necessarily compromises bearing life, due in part to elevated spring load. Attempting to add bearings, i.e., “duplex” them in order to improve load carrying characteristics of the individual bearings cannot be effectively accomplished with a spring-loaded system. This is due to the poor stiffness characteristics of the spring system. Typically, only one of the bearings will carry load while the second bearing simply “goes along for the ride”.
It is, therefore, an object of this invention to incorporate a system which provides a separate, cool-air stream to the bearing assembly, for the purpose of controlling bearing temperature rise.
It is another object of this invention to provide a cool-air stream to the backside (or backplate) of the compressor housing itself, such that temperature rise due to the compressed air stream is effectively prevented from progressing towards the critical bearing mounting locations.
It is another object of this invention to provide a separate cool-air stream to the belt drive system, including the tensioning and idler pulley system, with the effect of controlling temperature rise in the drive belt and the idler pulley-bearing assembly.
It is another object of this invention to incorporate a fully enclosed drive system with cooling air entry and exhaust ports purposefully positioned to enable an efficient and highly effective cooling system.
It is another object of this invention to design the drive system enclosure such that entering cooling air may further be screened or filtered thus preventing debris from entering the system.
It is another object of this invention to incorporate sound absorbing and attenuating materials with cooling-air entry filtration.
It is another object of this invention to design the enclosure such that noise absorbing material may be conveniently applied to the enclosure interior, and manage noise which is developed in the drive-belt system, resulting in quieter system operation.
It is a further object of the present invention to incorporate an improved spindle assembly, wherein a rigid pre-load design is implemented which enables the use of additional bearings to improve load carrying characteristics and operating life of the system.
The present invention accomplishes these objects and provides other related advantages.